IPTV (Internet Protocol TV) is a term used when delivering broadcasted TV-services over an IP network, typically a broadcast access network. In addition, more personalized service can be delivered due to the flexible nature of an IP network, e.g. video-on-demand or other user specific service, which then are delivered over unicast IP streams to the end user. IP video systems are becoming a key feature in service providers triple play offerings towards residential and business customers. Offering acceptable channel switching time with reasonable picture quality is essential for customers adoption. The problem maps directly into keeping low delays both in the customer premises and within the network.
To begin decoding and constructing an image from the video stream a lot of information needs to be gathered from the stream, which only comes with a certain frequency. In particular, to start displaying the image of a new video feed, the decoder needs to wait until a so-called intraframe (for a MPEG-2 codec) or a Random Access Point frame (for a MPEG-4/H.264 codec) arrives in the video stream. Intraframes are the only frames in the media stream that contain enough information on themselves to reconstruct a complete image. They typically come with a periodicity of 0.5 to 5 seconds, depending on the encoding type.
Existing solutions use a combination of pull mechanisms to obtain the last intraframe transmitted in the video transmission (HTTP GET or other) from the video server or the closest access node, or different mechanism to deliver slightly time-shifted video streams, so that the time distance to receiving an intraframe gets heavily reduced. These solutions imply that the channel switching mechanism will only be able to show a static image until the next intraframe arrives and the video decoding can continue or that your bandwidth consumption grows with the number of time-shifted streams that you are making available at the access node (DSLAM or equivalent). If the time shifting occurs in the access node itself, the requirements on processing power and capabilities of the multiplexing access node gets greatly enhanced.
Consequently, there is a need for mechanisms for reducing the channel switching time.